Motor driven tuning system



m, @IQ

NUON" m. u H. M W H H. H. BEIZER ET AL.

MOTOR DRIVEN TUNING SYSTEM Filed June 1v, 195s June 11,1940.

Patented June 11,1940

UNIT-ED STATES PATENT *l OFFICE MOTOR DRIVEN TUNING SYSTEM ApplicationJune 17, 193s, serial No. 214,390 4 claimV (o1. 17a-zas) The presentinvention relates to an electric motor control system particularlyadapted for tuning control of radio receiving apparatus and the like,wherein a, reversible ,electric motor is connected to drive a radiotuning device under control of circuit elements for causing the motor tomove the tuning means from one to another of several preselected tuningpositions.4

Motor tuning for radio receiving systems providing for remote controltuning and preselection tuning' has gone into more extended commercialuse with the advent ci recent automatic freouency control circuitswhich, as is' known, permit the oscillator frequency to ice adjustedcutolli motcolly to correct for inaccuracies in tuning adjustment in asuperheterodyne receiver.

utoniatic frequency control circuits ,toev corncertain receiving systemsand edd to if cost reore than desirohle. However, acci o' tuning isimportent, itis e, primary of the ove ent invention to provide c :cotosf qe particularly to e,

isle motor sv om in which the mon tor circuit is opened to lering' iVine' system to rest e. preselected position when eiectricei contact oureversing con'iinutotcr device, connected with. the tuning controlsho-it, reaches insulati segment 'between tivo refversing discs orsegments of the comrnutotor de vice.

i5 The accuracy of stopping depends upon the vv' oi the insulator orsegment and the rod-ius ci the oommutetor device at the segment and ispreferably such that the tuning syst/ern may stop for accurate tuningadjustment towithin one c. or' the desired signal frequency.

The matter of speed in tuning is also important and with accuratestopping, the necessity for higher speed in tuning may cause over-travelci the motor at the insulating segment and reversed of the motor and thetuning'. Although the overtravei may ce small in amount, even with an'armature of low inertia in the motor, it has been. difficult heretoforeto control the stopping for accurate tuning without oscillation orhunting.

It is therefore a further 'object of the present i invention to providea reversib'le motor tuning system for radio receivers which may providerel-4 atively high speed tuning movement while at the -same timeproviding accurate tuning adjustment 55 without hunting or oscillationabout the stopping point, whereby the necessity for automatic frequencycontrol circuits, and the like, may be eliminated. O

It is a still further object, of the present invention to provide animproved reversible motor tuning control system for radio receivingapparatus, and the like, which eiectively utilizes the reversing actionof the motor means to provide accurate tuning adjustment to preselectedtuning pol sitions.

It is an object of the invention, furthermore, to provide a reversiblemotor tuning control system 'for radio receivers, and the like, having areversing commutator device in which the insulating geo or segment ofthe device between the revers@ ing segments may loe ricade relativelynarrow for accurate tuning, vfhileat the same time providing high tuningmovement lov the motor means, without oscillation or hunting about thestopping positions The invention will, however, he better vendere stood'from the following description when cori-T4 sidered in coieoection withthe accompanying drawing and its scope will he pointed out the appendedcleiins.

f in the drovvins Figure i e. sclieniotic circuit 'divorcio tofgetherwith a diagrammatic Tfepresestation or" e. tuning system for a receiver,embodying the invention, and

Figure end view of e, mechanical detail. the system showoin l, and enlsreecl sco-ie.

Referring to the drawing, a, tuning system for o radio receiver or likeapparatus is diagrommoti call-f; represented by usual threesome varilaisle tuning capacitor, indicated at having* a tuning controlsiiait Eicoupled through a shaft l to o cord drive Wheel or drum 3, and at theop'- posite end through a shaft Q to a reversing comm mutator device iiicomprising two reversing contact segments ii and i2 and an insulatinggap or segment i3 therebetween. The vsegments il and i2 are connectedthrough reversing leads M, respectivelywith reversing windings i5 and i6of a reversible electric motor il.

The motor is 'energized from a suitable source oi low voltagealternating current, such as a sec ondary winding i8, on the powertransformer i9 of the radio receiver. One side of the secondary l isconnected through a lead 20 with avmain operating winding 2| oi' themotor, while the opposite side of the secondary is connected through alead'22 and a series of push-button selector switches 23-2'l, inclusive,selectively with one that the switches 22-2I, inclusive, are connectedin series when in the open position and the series circuit is completedto the potential supply lead 22 through the contacts of a multipleccntact switch 2l. This series circuit arrangement prevents more thanone selector button from becoming effective to operate the motor,thereby preventing overheating of themotor should it receive operatingturrent continuously through more than one selector switch and bothreversing windings at'the same time.

The motor circuit arrangement issuch that while the contact 20 is overthe insulating gap or segment 'the motor circuit is opened and the motoris deenergized following closing of the switch 25. The contact I0 whenclosed with the segment II energizes the reversing winding I6, causingthe motor to drive the tuning shaft I and the commutator device Ilthrough a gearing connection hereinafter described, in a 'direction torestore the commutator to the position shown, with the contact 30 at thegap I2. Contact with the segment I2 causes a similar movement in theopposite direction to restore the commutator to the position shown. Thusthe tuning is always brought to the same point of rest for each selectorswitch. l

l The contacts 28-32, inclusive, are movable or adjustable with respectto the insulating gap or segment ,I3 to cause the radio tuning device tostop in any one of a plurality of preselected positions corresponding todesired signals or radio stations to be received. In order to provide ahigh degree of accuracy in tuning, the segment Il or insulating spacebetween the reversing segments II and I2 must be relatively narrow asare also the contacts 28 to 32.

In a present preferred embodiment of the invention the insulatingsegment I3 is provided at the periphery of two hat metal plates, in theform shown at II and I2, mounted to rotate in connection with selectorcontacts 2l to 32, inclusive, located at a distance from the center ofrotation of from three to four inches, whereby a small degree of angularrotation provides a relatively wide range of movement for the insulatinggap.

With'this arrangement the width of the insulator or gap. has been set at0.75" and the diameter of the contacts has been set at .059"A whichpermits .008" on either side of each contact when it is centered on theinsulator i'or` an exactly tuned-in positionl of the tuning device.

It has been found that with a relatively small amount of over-travelwith an ordinary motor drive and with production tolerances in theinsulating gap varying from the values above given, and even when themotor armature has relatively low inertia, it is ldifficult to controlthe tuning without excessive oscillation or hunting about the stoppingpoint.

However, the accurate adjustment providedl bythe narrow insulating gapin the reversing commutator may be maintained and accurate stopping maybe provided without oscillation'or huntingif the driving motor isfurther controlled as will hereinafter appear.

The motor is of the shifting armature type, having anv armature 2lmounted on a shaft l! and axially movable therewith`when energized,against a spring 40 to cause a crank arm II carried by the shaft toengage between the teeth I2 (Fig. 2) of a star wheel l2 which is mountedon a driving pinion 44. The pinion M forms part of a. gear train "-48connecting the star wheel 43 with a tuning control shaft 41 for manualtuning and having a suitable tuning control knob The shaft ,l1 isconnected with the drum 8 through a, cord drive indicated at 4S, and asimilar cord drive indicated at 50. is also connected with the drum orsheave 8 to actuate a. tuning dial pointer or indicator 5I, in

' connection with a tuning indicator dial shown When the motor amatureis energized the crank arm il engages the star wheel l2 by means of thecrank pin and drives the gear train l4l-li which in t-urn drives thetuning control shaft The tuning control shaft is connected to thevariable tuning vdevice 5 through the cord drive which provides areduction ratio of 17:1, for example. The reduction ratio from the motorshaft to the tuning control shaft l1 may be substantially`25z1. Withthis reduction and a. present available type of motor, the time requiredto tune from one end of the broadcast band to the other is approximatelythree seconds. When lthe motor is deenergized the armature is thrownclear of the star wheel and pinion by means of the spring 4I, thearmature itself having axial. movement, as hereinafter referred to. t

A flywheel 6l mounted on therrear end of the motor shaft 29 between stopwashers indicated at 6I is free to rotate on the shaft but is preventedfrom axial movement with respect to the shaft by the washers. Theflywheel provides an inertia weight or device for imparting axial androtational inertia to the drive system and preferably, as shown, to themotor shaft.

Driving torque is transmitted to -theflywheel from the shaft through afriction plug indicated at I2 in a radial recess Il in the fiywheel. Theplug is pressed against the shaft by a suitable spring 6l. Ihe frictionplug may be of leather and the pressure on the shaft is controlled bythe screw 05. The action of this ywheel controls the over-travel of themotor and the accuracy in the direction of the corresponding station orI selector contact such as the contact 3L Ihe motor cannot come up tospeed immediately because of the friction load of the slipping flywheelwhich provides a momentary overload but does so as soon as the inertiaof the flywheell is overcome.

W'hen the insulator I! on the selector disk reaches the station contact3l, for example, both the motor and nywheel are rotating at the samespeed and the combined inertia carries the tuning mechanism and theinsulating segment past the'stop position and the contact 2l, therebycausing the motor to reverse. Because of the momentum of the flywheel lwhich is still rotating in the original direction, and the frictionbetween the ywheel and the shaft, the motor speed in reverse is reduced.

f While the Imotr is rotating at low speed in the `hold the armature inthe forward position and to maintain the crank arm in engagement withthe star wheel during this brief interruption, thereby preventingdeclutching and lost motion y in the reverse driving action of themotor.

Adjustment of the set screw 65 on the flywheel friction pad controls theamount of over-travel and the accuracy of tuning. In order to ensurethat the motor may provide final tuning while rotating very slowly, thedrive pinion 4l has been provided with a multiple bladed star wheel, asshown in Fig. 2, which permits the motor to start Areversing the tuningshaft immediately before the motor attains speed, which would cause theselector to over-travel the selected contact and hunt or oscillate.

With the reversible motor tuningvsystem described, it will be seen thatthe reversing commutator may be provided with a relatively narrowinsulating segment between the reversing disks or ksegments and on arelatively long radius providing accurate stopping and eliminating thenecessity for automatic frequency control nf the oscillator.

Furthermore, the tuning system may be made to operate at a relativelyhigh speed, that is, it may have a relatively high rate of tuningmovement, together with accurate stopping with the commutator deviceabove referred to, by providling the ytuning motor with a flywheelfrictinallyi` connected with a shaft driven by the motor, preferably themotor shaft itself, as shown, which applies a rotary braking effect tothe motor when the latter is reversed. The friction between the iiywheeland the shaft is adjustable and starts the flywheel spinning in theinitial direction so that when the motorl reverses because of overtravelat high speed, the motor armature .must turn against the friction loadof theoppositely rotating frictional flywheel. This provides an overloadwhich causes the motor to start up much more slowlythan it wouldotherwise and the rate of speed increase is controllable by means of thefriction load provided by adjusting the 'set screw 65.on the flywheel.Therefore, it is possible to cause the motor to stop within a muchsmaller angle and with a much narrower insulating gap in the electricalstopping device.

Furthermore, with the flywheel mounted on the motor shaft between fixedcollars or other suitable means, it may not only rotate to provide afriction load on the shaft for controlling the tuning, but it may alsoprovide axial inertia in a shifting armature type of motor'suflicient tovcause the clutching means to remain engaged during the deenergizing andreversal of current to the motor, as the stopping' device contact trav.

erses the insulating gap or segment during the over-travel movement ofthe tuning operation.

This prevents vunnecessary axial movement or chattering of the motorarmature at each tuning point.

We claim as our invention: Y 1. In an electric motor control system forradiov apparatus and the like, the combination with a control device ofa reversible electric motor hav ing a rotatable drive shaft connectedwithsaid device to operate it, said shaft being axially movable inresponse to the deenergizing of the 4motor, means carried by said shaftproviding a clutch operable upon axial movement of said'` lshaft todisconnect the shaft fromsaid control device, a ywheel frictionallymounted on said shaft whereby said flywheel imparts axial inertia tosaid shaft tending to resist axial` movement and a frictional load4 onsaid shaft to reduce the initial speed of rotation upon reversal of saidmotor by reason of the continued rotation of said flywheel in theinitial direction and fric- ,1li

tion between said flywheel and said shaft.

2. In a motor-driven radio tuning system, the combination of a driveshaft, tuning means having a movable element connected with the shaftand operative at -a lower speed than the drive shaft, electricalmeans'includng an adjustable device for deenergizing the motor at apreselected position in the tuning movement of said element and forenergizing said motor to move said element toward said position fromeither side thereof, afiywheel device frictionally coupled to and drivenby the motor whereby said device .is adapted to coast when said motorreverses the direction of rotation, to provide a braking load for and toreduce the speed of the motor in reverse, means providing a clutch inthe connection between the motor and the movable tuning element, saidclutch having an operating element connected with the flywheel device tomove conjointly therewith axially in response to energizing anddeenergizing of the motor, whereby the axial inertia of said devicetends to resist momentarily the operating movement of said clutchelement.

3L In a radio tuning control system, a tuning shaft, a reversibleelectric motor having a rotary drive shaft which moves axially inresponse to the energizing of the motor, means providing a restoringforce for said shaft against which it moves, means connected with thetuning shaft for reversing the rotation of said motor followingover-travel of and for stopping the motor at the same initial ,speed asin a forward direction when energized, by reason of 'rotating frictionload imparted to said motor shaft by said device,

thereby to effect exact stopping of said tuning shaft at any one ofvsaid positions, and means providing a connection between said device andsaid shaft for imparting said axialinertia to said shaft.

4. In a motor tuning system for radio receivers, the combination with atuning shaft, of a reversible tuning motor having `a shaft connectedtherewith, a clutch in said connection, a reversing device for the motorconnected with said shaft and comprising two contact elementsseparatedby a relatively narrow insulating gap, at least one adjustablecontact 'element positioned to engage sait/l` segmentsland lyingin thevpath of movie'- ment of said insulating gap, said contact being slightlyless in width than said gap, a reduction gearing between said motor andsaid tuning shaftrproviding a high rate of movement for said shaft suchthat the gap over-travels said Contact causing reversal of said motor, aiiywheel providing a frictional load against rotation of said motor uponreversal to reduce the speed of said motor, whereby said contact may becentered accurately on said insulating gap at the reduced speed, saidywheel being mounted on the motor shaft to rotate relatively thereto,

means providing an adjustable-friction connection between said iiywheeland said motor shaft whereby the initial speed of the' motor uponreversalmay be continued, means for operating said clutch by axialmovement of the motor shaft,

and means providing a connection between the flywheel and the motorshaft tor applying the inertia load of the flywheel to the shaft inresponse to axial movement thereof.

HAROLD H. BEIZER. WILLIAMENEWHAN.

